The invention relates to cleaning hard surfaces, particularly plastics, dried paint, and other surfaces for which the chemical substance or substances that constitute the surfaces are insoluble in, and not damaged by contact with, water and usually are predominantly organic.
Current and prior art in this field generally relies on cleaning surfaces initially with organic solvents and/or with a variety of aqueous solutions that usually contain wetting agents, other surfactants to disperse oily and waxy soils, and alkalinizing or acidizing agents. These initial liquid cleaning compositions are usually brought into contact with the surfaces to be cleaned by immersion or relatively gentle spraying of the liquid cleaning composition onto the solid surface to be cleaned. Such methods are usually effective for cleaning most metals, in part because the aqueous solutions used can be and usually are formulated to slowly dissolve the metal surface being cleaned, thereby detaching much of the soil by dissolving the part of the surface to which the soil is attached. No suitable analog of such aqueous solutions that is effective on most organic surfaces is known, however. Accordingly, in cleaning organic surfaces reliance must be placed primarily on the chemical nature and temperature of the chemical cleaner liquid, and, to some extent, on agitation, spray impingement, or other mechanical means that will cause relative motion between the cleaner liquid and the surface to be cleaned. (Although one of the rinsing stages often used in cleaning plastics is generally called “power rinsing” or “power washing” and is in fact somewhat more effective than ordinary rinsing, neither its mechanical force nor any other characteristic of the rinsing, as contrasted to the cleaning, stage of a typical industrial cleaning process has been found in practice to contribute significantly to fine particle removal; these particles must be removed by the end of the exposure of the surface to a chemical cleaner, or they normally will not be removed at all.) Prior art chemical cleaners have proved satisfactory for many purposes, including much cleaning of plastic articles prior to painting them.
Cleaning of plastics for some uses, however, has not yet been satisfactorily achieved by these means of the prior art. For example, plastic headlight housings for automobiles are often sputter coated with metal after the housings have been cleaned, in order to create a parabolic reflective surface that will focus toward the forward direction the beams of the headlight later installed in the housing. No cleaning technique available from the prior art has been found to be entirely satisfactory for this use. Other examples of dissatisfaction with currently available techniques for cleaning surfaces exist in the electronics and aerospace industries.
Accordingly, an object of the present invention is to provide satisfactory cleaning of hard surfaces by liquid cleaners in instances in which currently available methods are not satisfactory because of their inability to remove fine particles from the surface cleaned.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, “parts of”, and ratio values are by weight or mass; the term “polymer” includes “oligomer”, “copolymer”, “terpolymer” and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word “mole” means “gram mole”, and the word itself and all of its grammatical variations may be used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; the term “paint” and all of its grammatical variations include all materials known by more specialized names such as “lacquer”, “varnish”, “shellac”, “primer”, “electropaint”, “top coat”, “color coat”, “clear coat”, “autodeposited coatings”, “radiation curable coatings”, “cross-linkable coatings”, and the like and their corresponding grammatical variations; and the terms “solution”, “soluble”, “homogeneous”, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained within the range of 18–25° C.